This longitudinal study of individuals with sex chromosome abnormalties is the first in the world to follow propositi from birth to adulthood. Propositi, now in their twenties and thirties, include men with an extra X chromosome and women who have an extra X or are missing all or part of an X chromosome. Intellectual skills are reduced somewhat in all three of these groups, but most reduced among the women with an extra X chromosome. Some specific learning problems, seen previously in childhood, persist into adulthood. Thus, many propositi have difficulity with reading, particularily the men with an extra X chromosome. Women missing an X chromosome tend to have difficulity with spatial thinking and arithmetic. Psychiatric difficulty is also increased in these groups, most dramatically in the women with an extra X chromosome. Still, many of these individuals function well and have no psychiatric problems. The current study has included magnetic resonance imaging brain studies. Preliminary results reveal some subtle neuroanatomic changes in individuals with sex chromosome abnormalities, including reduced frontal, temporal and occupital lobe size among women missing an X chromosome; reduced left temporal lobe size among men with an extra X chromosome; and reduced overall brain size, as well as right temporal lobe size, among women with an extra X chromosome. These results are preliminary and the study is ongoing.